1. Field of the Invention
This invention relates generally to blow molding. In particular, this invention relates to mold assemblies for blow molding.
2. Description of Related Art
Blow molding is a cyclic process wherein a parison of material in a moldable condition is centered on the parting plane of a mold assembly, the mold assembly is closed around the parison, the parison is expanded so the exterior of the parison abuts molding surfaces defined by the closed mold assembly, the blow molded article is conditioned to be sufficiently rigid to retain its size and shape while unsupported, the mold assembly is opened and the blow molded article is removed. In general, the moldable condition of the parison is achieved when the material of the parison is at an elevated temperature, and the rigid condition of the blow molded article is achieved when the temperature of the material has been reduced. A blow molding machine comprises a press for opening and closing the mold assembly and blowing means for introducing a pressurized fluid (typically air) to expand the parison in the mold assembly. Alternative types of blow molding equipment produce blow molded containers from preformed parisons typically produced by injection molding away from the press (so called “two-stage” blow molding) and from parisons extruded at the blow molding press (so called “single-stage” blow molding), Two stage blow molding machines typically include means for mechanically stretching the parison longitudinally during blow molding. Additionally, blow molding machines may comprise means for handling the molded article upon removal from the mold assembly, means for trimming waste from the molded article (single-stage machines only), and heat transfer devices to elevate the temperature of the parison to achieve the moldable condition and to reduce the temperature of the blow molded article to achieve the rigid condition.
Blow molding is commonly used for production of containers wherein the blow molded article comprises a body portion defining a closed end and a neck portion connecting the body and a mouth opening for filling the container and dispensing the contents therefrom. Advantageously, the neck portion of the container comprises an exterior surface having a feature, such as a thread, called the “neck finish” for engaging a separable closure. In two-stage blow molding, the neck finish is completed during production of the preformed parison, and in single-stage blow molding, the neck finish is formed by mold components upon closure around the extruded parison. Mold assemblies for blow molding containers comprise mating mold components wherein molding surfaces open to the mating faces of the mold components define the exterior of the container. To accommodate containers having a range of volume compatible with a particular mold assembly, each mold component advantageously comprises a replaceable height insert between the neck portion and closed end and defining the longitudinal extent of the article to be molded. In known mold assemblies, disassembly of the mold component is required to insert or remove the height insert, including removal of fasteners used to retain the height insert in the mold component. Hence, there is a continuing need for mold components comprising height inserts which may be removed or installed without removal of other elements of the mold component.